Truck mounted brake systems are known in the prior art. More particularly truck mounted brake systems based on variable ratio levers have been described in the prior art such as Polanin et al U.S. Pat. No. 3,207,271. Such systems have been fabricated using power units of the type manufactured for the automotive industry, such as those manufactured and sold by Bendix-Westinghouse Automotive Airbrake Company under the trade name "ROTOCHAMBER". These power units, as described in the Polanin et al patent comprise a plate secured to the inner end of a piston rod which is engaged to the inner periphery of a flexible diaphragm, which has its outer periphery secured to the cylinder. The effective area of the cylinder is determined by the convolution of the diaphram. Such cylinders provide no transverse support for the inner end of the piston rod.
The power units are suspended from the bolster. In this configuration, the power units are subjected to constant vibration. Because the "ROTOCHAMBER" type of power unit provides only a single bearing surface for the piston rod (the other end being attached to a flexible diaphram) a number of failures have been found, as exhibited by scored piston rods and center boss bushings.
Further, because the prior art "ROTOCHAMBER" power units rely on flexible diaphrams, the effective working area is limited and in order to provide adequate working area, a relatively large diameter "ROTOCHAMBER" is required. Although brake cylinders of relatively large diameter were not a problem in the railway cars being produced in the 1960's, the availability of high strength steel has changed the design of freight cars. Today, freight cars with a capacity in the 70 to 100 ton range which weigh as little as 25 tons (50,000 lbs.) are perfectly feasible. However, the larger capacity cars require the use of springs which have a greater deflection. When loaded to capacity, such high capacity cars cause the springs to deflect to the point that very inadequate rail clearance is provided for brake system based on diaphram-type cylinders. Accordingly, brake cylinders of reduced outside diameter for a given effective area are required.
The brake system of the present invention is designed to overcome the problems of the prior art and provide the brake system which may be employed in the modern high capacity cars, as well as new cylinders which may be installed in the older cars as replacements for the existing brake systems and which meet current requirements of performance based on industry standards.